1. Field of the Invention
The present invention relates generally to a method of joining and repairing composite materials and, more particularly, to a method of joining and repairing composites which includes interlocking the two pieces to be joined and/or repaired.
2. Description of the Related Art
As the material sciences advance, more vehicles and consumer parts are being manufactured of composite materials. However, these composite materials have experienced problems in manufacturing and during repair because they are difficult to adhere to one another in addition to being difficult to adhere to other materials. For example, in the automotive context, a fiberglass reinforced thermoset plastic part (FRP), such as a front quarter panel, needs to be adhered to a metal part, such as the vehicle chassis. Joining the FRP to the metal is difficult because they are two unlike materials.
On the other hand, in the event that the vehicle is involved in an accident, the front quarter panel may become punctured or otherwise damaged. In this event, repair or replacement is necessary. Again, to join a composite piece (the repair piece) to the damaged piece requires composite joining. To maintain the original strength and integrity of the damaged part, new methods are required for joining the two composite pieces.
Consequently, among the primary problems encountered with repair and joining of composites to other materials is either restoring the original structure to a condition where the physical properties such as tensile strength, compressive strength, bending strength and the like would approximate that of the original undamaged structure, or in the alternative, that the originally joined manufactured parts could easily be joined together in a manner that would provide a strong joint.
Therefore, it would be advantageous to provide a method for repairing and joining composite materials while providing nearly original strength, or 100% restored strength.
Conventional methods of repairing composite materials include scarfing, or abrading, an area near the damaged portion, filling the void created by the scarfing with a resin, and applying a patch on top of the resin filled void and allowing it to cure. The patch may be plane-woven, or a fiberglass filler chopped up and slurried into the resin to act as a reinforcement in the patch. If the patches are placed on both sides of the damaged area, on top and underneath the damaged zone, this is referred to as a "double lap joint" repair. Prior repair techniques to this describe woven fiberglass cloth swatches being bonded to a fiberglass structure at the points of discontinuity (where the damage occurred) in such a manner that the stresses, which normally would accumulate at the severed ends of the glass filaments in the original structure, were transmitted through the glass cloth of the patch. Although this method overcame the problem encountered where a concentration of stresses at the defect site normally resulted in the complete rupture of the fiberglass, the rupture occurred at an undesirably low stress level. The greatest advantage of the present invention over the prior art methods is that the rupture at the damaged area will occur at a much higher stress level. Another problem is introduced by applying isotropic glass cloth (that is, a cloth having the same physical strength in all directions) to anisotropic materials, i.e. those materials which have unequal physical properties along different axes (such as a woven cloth having its greatest strengths at the 0.degree. and 90.degree. orientations along the warp and fill directions).
Typically, metals are isotropic because they have the same strength in all directions. Composites, made up of plane-woven fiberglass mats, are considered anisotropic because they exhibit their greatest strength in two directions. For instance, most fiberglass plane woven mats that are saturated with resins acting as patches for fiberglass repair have strengths in the 0.degree. and 90.degree. orientations, i.e. or following the warp and fill thread directions in a square weave cloth. A new method of joining would be especially helpful in bonding isotropic to anisotropic materials, such as bonding plane woven mat composites to random fiber composites, metals or other thermoset plastics.
Furthermore, it would be advantageous to provide a method for making pre-assembled manufactured parts having specific bondline configurations which would later on facilitate interlocking of those parts for better joining. For example, if a fiberglass part and a metal part which were to be joined together were originally manufactured with the bondline configurations set forth in the invention hereinafter, a manufactured part could be joined via the method of the present invention to provide a manufactured part having great strength and flexibility.
It would also be advantageous to provide a method for composite joining which would reduce the stress concentration at the bondline, thereby increasing the contribution of the reinforcement patch to joint strength. In basic terms, it would help the strength of the double lap joint patches if there was an additional contribution to the bonding. That additional contribution is the subject of the present invention.